The present invention relates to a gauge line position measuring device, a program for measuring a gauge line position, and a gauge line mark in order to measure the gauge line position in a test piece by a non-contact video method.
Conventionally, when a mechanical load is applied on the test piece by a material testing machine, a gauge line position is optically detected. As a gauge line sticker which is put on a gauge line of the test piece, for the simplest example, a sticker with a linear gauge line mark in a direction orthogonal to a displacement direction of the test piece is known. However, in a mere linear gauge line mark, even if shading data by pixels are integrated in the direction orthogonal to the displacement direction of the test piece, it is well-known that it is impossible to obtain a stable measurement accuracy.
Therefore, currently, by improving the mere linear gauge line mark, when the image data are integrated in a direction orthogonal to the displacement direction of the test piece, an interpolating calculation including a number of pixel pitches is possible (refer to Japanese Unexamined Patent Publication (TOKKAI) No. H11-94719). Specifically, by using an improved gauge line mark wherein a black portion and a white portion are clearly distinguished and integrating the image data in a direction orthogonal to the displacement direction of the test piece, a profile P(x) regarding a coordinate x indicating the position of the test piece is obtained, and the gauge line position is computed from two x coordinate values wherein the profile value intersects to a predetermined threshold.
However, even if the above-mentioned improved gauge line mark is used, the interpolating calculation by the pixel pitches is limited to obtaining a measurement resolution of approximately a few to a few tenth of an interval between image elements. Specifically, since a black-and-white gauge line mark is imaged by a video camera, the measurement resolution could not be improved by conducting the interpolating calculation between the image elements.
Accordingly, an object of the invention is to provide a gauge line position measuring device which can accurately measure a gauge line position in a test piece.
Further objects and advantages of the invention will be apparent from the following description of the invention.